1. Field of the Invention
The present invention relates to a video watermarking apparatus and method. More particularly, the present invention relates to an apparatus and method of watermarking a video in a compression domain, substantially resisting recompression of the video.
2. Description of the Related Art
Generally, due to the widespread use of digital media and various multimedia data transmission and storage devices, and the development of authoring tools, multimedia data may be easily copied and distributed via a network. Therefore, new services are being provided. However, a problem of adequately protecting the copyright of the digital media has seriously escalated.
Watermarking is used for protecting the copyright of digital media. Watermarking is a method of inserting a watermark, which is a signature of an author or information identifying the author, into the digital media. The watermark is to solve the problem of protecting the copyright of the digital media by inserting the watermark into the digital media so that when a problem of proving copyright infringement occurs, the watermark may be extracted to show proof of copyright ownership.
Methods of watermarking may be classified into a method of watermarking in a spatial domain, and a method of watermarking in a compression domain.
Since various algorithms may be applied to conventional methods of watermarking in the spatial domain, it has the merit of substantially resisting various attacks.
However, most video is encoded while stored and transmitted. Therefore, to apply the method of watermarking in the spatial domain, an entire encoded video has to be decoded and the decoded video has to be encoded again after inserting a watermark into the decoded video. This presents a cumbersome problem of inserting the watermark and encoding the decoded video again. Also, there is a large amount of computation required by a process of decoding the entire video.
As a method of reducing the large amount of computation, watermarking in the compression domain is provided, which operates in a bit stream of the compression domain. However, in conventional methods of watermarking in the compression domain, since a watermark is directly inserted into/extracted from an encoded discrete cosine transform (DCT) coefficient, there is a problem of being relatively ineffective against a recompression attack of a video.
As representative examples of conventional methods of watermarking in a compression domain, there are Hartung, Cox, and Langelaar methods. The Hartung method, disclosed in U.S. Pat. No. 5,915,027, has a disadvantage of requiring a large amount of computation because a very complex circuit is required for preventing error propagation and an increase of bit rates.
In the Cox method, disclosed in U.S. Pat. No. 5,915,027, since an inserted watermark affects only frequency features of data in a compression domain, it is subject to a simple and effective attack when there is a change in bit rates and frame structures. Also, recompression of a video and additional computation caused by shaping of the watermark is required.
In the Langelaar method, mentioned in U.S. Pat. Nos. 6,768,980 and 6,748,362, very quick computation is possible in a compression domain but there is a disadvantage of having a structure that is very weak in a recompression of a video.
Accordingly, there is a need for an improved apparatus and method for inserting a video watermark in a compression domain.